The present invention relates to water heating systems.
It is known to heat water by using a single storage reservoir or hot water heater which includes both a conventional heating means as well as a heat exchanger connected with an alternate source of heat, such as a solar collector. A disadvantage of such systems is that the water heater must be specially fabricated to accommodate solar energy heating components, which adds considerable expense and complexity to the system. Also, a single tank has a limited energy storage capacity, and since solar energy is irregular and intermittent throughout any day as well as throughout any year, it often happens that stored solar energy is insufficient to meet water heating demands, with the result that increased amounts of utility or conventionally supplied power must be relied upon to heat the water.
The disadvantages of a single tank system may be alleviated somewhat by using two separate tanks or reservoirs set in series. The first has a heat exchanger therein which is connected to a solar collector, and the second may have an electric or gas heater. Cold water enters the first tank wherein it is preheated, and thence passes into the second tank for being additionally heated, if necessary, prior to flowing to a point of delivery. However, a major disadvantage of conventional two tank systems is that there usually is no arrangement, except during extraction of hot water or by mechanical pumping, for transfer of hot water from the first tank to the second, so that if the water in the second tank is not at a sufficient temperature for the needs of the user, it is substantially heated constantly through use of expensive energy supplied by a utility company.